1. Field of the Invention
The present invention relates to a shadow mask frame assembly for a cathode ray tube suitable for a shadow mask, and more particularly, it relates to a shadow mask frame assembly for a cathode ray tube for enlarging an useful screen and easily assembling and disassembling a shadow mask to a mask frame.
2. Description of the Prior Art
In a color cathode ray tube having a shadow mask, R, G, and B electron beams emitted from an electron gun are converged, passed through apertures of a shadow mask, and landed on R, G, and B phosphor, and thereby realizing colors.
The shadow mask is disposed in a position adjacent to a phosphor.
FIG. 3 shows a general structure of a conventional mask frame.
In FIG. 3, a shadow mask 1 comprises an approximately rectangle-shaped useful screen portion 5 having apertures 3 through which electron beam passes and a skirt portion 7 formed by approximately perpendicularly bending a border of the useful screen portion 5 having apertures 3.
Referring to FIG. 4, the skirt portion 7 of the shadow mask is welded inside a mask frame 9.
The mask frame assembly which the shadow mask 1 is welded inside dispose the shadow mask 1 at a predetermined space from a phosphor layer 17 coated on the inner circumference of the face panel 11 by engaging a stud pin 13 fixed on an inner circumference of the face panel 11 with a hookspring 15 welded outside the mask frame 9.
The mask frame 9 must have mechanical intensity enough to support the shadow mask 1 at tightly strained state.
The mechanical intensity of the mask frame 9 increases in proportion to the thickness, however, since the weight becomes heavy when the thickness is thickened, a bead 19 is generally used to obtain the maximum mechanical intensity with maintaining the minimum thickness.
In addition, the bead 19 is a portion to which the skirt portion 7 of the shadow mask 1 welded. For such a reason, the size of the shadow mask 1 is restricted not to increase the width of the useful screen portion 5 having apertures 3, and since the skirt portion 7 of the shadow mask 1 is spot welded to the bead 19 of the mask frame 9, the shadow mask 1 is easily vibrated to occur howling when the impact is applied from outside.
In such a structure that the shadow mask 1 is easily resonated, the deterioration of the image is not avoidable since the large-sized cathode ray tube recently manufactured has a high-power speaker.
In another aspect, as shown in FIG. 5, a burring 21 is formed on an open end portion of the mask frame 9 to enlarge the area welded to the shadow mask 1 with maintaining the mechanical intensity.
However, since the burring 21 is outwardly bent from the open end portion of the mask frame 9, the burring 21 is obstructed by the stud pin 13 when mounting the mask frame 9 inside the face panel 11.
To avoid the interference between the stud pin 13 and the burring 21, the size of the mask frame 9 is restricted to reduce the useful screen of the shadow mask 1.